1. Field of the Invention
The present invention relates to a mobile communication system, a radio base station controller and a transmitting and receiving power control method therefor, and more particularly to a transmitting and receiving power control method in a CDMA (Code Division Multiple Access) system.
2. Description of the Related Art
Conventionally, in a CDMA radio access system, a number of radio base stations and mobile terminals make the communications by setting up the link at the same frequency, whereby a receiving power (desired wave power) of signal in a certain line may interfere with another line and become an interference wave power. Therefore, in a satellite uplink in which the mobile terminal transmits and the radio base station receives, if a desired wave power exceeds a predetermined value, the interference wave power is increased and the capacity of line is decreased.
In order to solve this problem, in the conventional CDMA radio access system, a method for increasing the capacity of uplink by preventing the use of excessive transmitting power in transmission from the mobile terminal to the radio base station has been offered (e.g., refer to patent document 1).
With this method, the radio base station compares the receiving quality of a transmitting signal from the mobile terminal with the target receiving quality, in which an increased amount of transmitting power at the radio base station is decided based on its comparison result, the increased amount is added to the transmitting power at the radio base station upon a control instruction transmitted from the mobile terminal, and a control instruction for controlling the transmitting power at the mobile terminal is transmitted by the added transmitting power.
[Patent Document 1]
    Japanese Patent Laid-Open No. 2001-119342 (pages 19 and 20, FIG. 5)
In the above-mentioned conventional CDMA radio access system, the user is discriminated according to the code at the same frequency, whereby one mobile terminal or radio base station is affected by interference powers from other users, so that the communication quality is deteriorated.
That is, if the high quality communication tries to be made, the transmitting power of the radiobase station or mobile terminal is increased, and the interference power is increased at the same time, so that the maximum number of accommodating the mobile terminals at one radio base station is decreased. If the number of accommodating the mobile terminals is increased, the power assigned to each mobile terminal is smaller, resulting in a problem that the communication quality is deteriorated.